The present invention relates to thermo transfer type matrix printer for line-for-line printing and composing individual characters from dots by means of and in accordance with the thermo-transfer principle; the printer is to include a cylindrical printing drum, having a length which at least approximates the length of a line to be printed, and having a surface composed of heatable matrix "points" which can be controlled serially as well as in parallel as for groups of points sequentially .
Thermo printers in the most general sense to which the invention pertains can be classified as follows. In one instance thermo printing is obtained by means of thermo sensitive paper under utilization of a heatable printing head and through heating of selected spots of the paper so that the heated spot will discolor and assumes a contrasting appearance. A second type also called thermo transfer printing a wax layer containing a dye or ink is molten through a carrier foil under utilization of a heatable printing element and that part is then transferred upon regular paper. A third version is called an electro transfer printing process wherein an ink ribbon is used for carrying a wax layer with a dye or ink, the ribbon includes also a carrier foil, a metallic, i.e. electrically conductive layer, and a resistance layer with low electrical conductivity. By means of slide contacts the resistance layer receives current and is thus heated and the dye-wax layer is molten. The electricl conductive layer serves as general electrical return path.
The electro transfer method is disadvantaged by the fact that one needs a ribbon of particular and special construction. The used-up spots of a thermo ink ribbon are not subject to regeneration so that the use of such kind of ribbons becomes very expensive.
A so-called thermo transfer matrix printer is known, for example, through German Pat. No. 1,549,911. A printing device is proposed using only a very small number of slip rings. These slip rings are provided to transfer digital data including print data clocking signals, gate control, gate clocking etc. to a rotating device (drum) with a periphery being comprised of individual semiconductor/heating elements. These elements are selectively heated. Heat sensitive paper is run over the drum in order to benefit from a looping angle of at least 180 degrees. In this case then one does need a special kind of paper.